The present invention relates to electrical actuators for operating a mechanical device, such as valves and dampers; and more particularly to techniques for automatically determining the range of travel for the device.
Many types of mechanical devices are operated by an electrical actuator which moves components of the device between two extreme positions. For example, the damper in a heating, ventilation and air conditioning (HVAC) system may employ an electric motor to move the damper plate between fully opened and fully closed positions. In other mechanical systems, an electric motor opens and closes a valve to control the flow of a liquid. It may also be desirable in some applications to place the damper or the valve at various positions between fully open and fully closed to provide a variable flow of air or liquid.
The mechanical linkage of different types of valves and HVAC dampers require different amounts of rotation to move them between the fully opened and fully closed positions. For example, the mechanical configuration of some HVAC dampers require only 45.degree. of movement to move the damper between those extreme positions, while other dampers require 60.degree. or 90.degree. of movement. Universal actuators are available which rotate their output coupling a maximum of 95.degree., thus being able to accommodate several types of dampers. Employing a universal actuator eliminates having to stock a variety of actuators specifically designed for each type of mechanical device being driven. However, in order to properly operate a particular damper, the HVAC controller must be configured with the amount of travel or movement that the actuator has to provide to move the mechanical device between its extreme positions. That configuration also enables the controller accurately to place the damper at various desired intermediate positions.
Previously the controller was configured manually with the appropriate amount of rotational movement required by the associated damper. Such manual configuration was time consuming and prone to human error. In addition, the controller had to be reconfigured periodically to compensate for wear of the mechanical device.